1. Field of the Invention
This invention relates to a numerically controlled lathe, and more particularly to a method for operating such lathe.
2. Description of the Related Art
In a numerically controlled lathe, a machining table upon which a machining tool is disposed is also numerically controlled, and a structure of such existing machining table is shown in FIG. 4.
Although not illustrated in detail in FIG. 4, a bed 10 of the lathe is equipped with a known main spindle, and this spindle rotates a workpiece with the workpiece held. In FIG. 4, the center axis of the main spindle is designated by a reference symbol O.
Furthermore, a slide table 11 is placed on the bed 10 in such a manner that the slide table can traverse in a direction parallel to the spindle or normal to this page.
On the slide table 11 is positioned a ball screw 14 rotatively supported by brackets 12, 13. This ball screw is rotated by a servo motor 16 fixed to the slide table 11 with a bracket 15, whereby it is possible to move a tool, described in later, to an arbitrary position with respect to the main spindle.
An axis of the servo motor 16 is connected with the ball screw 14 by means of a coupling 17.
A ball nut 18 is provided so as to establish an engagement with the ball screw 14, and is disposed on the carriage 20 by means of a bracket 19. On the carriage 20 is supported a capstan rest 22 rotatively and is placed in position by means of a support 21 interposed between the carriage and the capstan rest. A given tool 24 is placed on the capstan rest by a bite holder 23, and the tool 24 such as a bite, etc., is ordinarily positioned in such a manner that a cutting surface of the tool 24 is aligned with the plane of the center of the main spindle.
Accordingly, when any given instruction for tool position is issued to the motor 16, it becomes possible to travel the tool 24 to a desired position in connection with the center 0 of the main spindle.
However, in accordance with the above-described conventional numerical controlled lathe, when a mass production is carried out for workpieces having a simple shape or a non-circular machining is performed, there has been drawbacks in that parts of the machining table which make a sliding contact are locally worn out because the carriage 20 repeatedly makes a reciprocating motion within a limited short range. Particularly, it has been a problem in that a part of the ball screw 14 is unevenly worn out, though the rest of the part maintains a sufficient accuracy. With this result, in view of the overall structure of the lathe, the mechanical life of the machining table is extraordinarily shorten by the aforementioned local abrasion of the parts.
Another drawback, in accordance with the existing numerically controlled lathe, lies in that since all of the elemental parts from the carriage 20 to the tool 24 make a high speed reciprocating motion, and since the inertia of the parts becomes large, there is a limitation for increasing the traverse speed of the parts.